JP 2008-75827A (corresponding to US 2008/0073605 A1) describes a fluid control valve arranged in a secondary air feed system that warms up a three-way catalyst at a time of starting a gasoline engine. Specifically, secondary air generated in a secondary air pipe is introduced to a three-way catalyst converter corresponding to an exhaust gas cleaning apparatus. The fluid control valve integrally has an electromagnetic valve which opens and closes a secondary air passage defined inside the housing, and a check valve that restricts fluid such as exhaust gas from flowing backwards to the electromagnetic valve and an electric air pump inside the system.
The electromagnetic valve includes a housing, a valve, a coil spring, and a seal rubber. The secondary air passage defined in the housing integrally has a valve seat. The valve reciprocates in the axial direction to approach or separate from the valve seat. The coil spring biases the valve in a valve-closing direction. The valve constitutes a valve object which approaches or separates from the valve seat to close or open the air passage. The electromagnetic valve has a valve head and a shaft part. The valve head has a flange shape and is received in the housing to be able to open and close. The shaft part has a cylindrical shape straightly extending to an actuator from the central part of the valve head, and reciprocates in the axial direction.
The seal rubber mounted to the outer periphery part of the valve head has a ring part opposing to the valve seat and a seal lip projected toward the valve seat. In the cross-section, the seal lip has a taper shape inclined to the axis of the valve so that the tip end is located on the radially outer side of the root end. The seal rubber has plural load receptacle parts on the inner side of the seal lip. The projection length of the load receptacle part is smaller than that of the seal lip. The load receptacle part receives the load of the valve by contacting the valve seat when the valve is fully closed. At this time, the seal lip is elastically deformed to bend toward the outer periphery of the valve and is in the tight contact with the surface of the valve seat, when the valve is fully closed, such that a clearance between the valve head and the valve seat is certainly closed.
When the seal lip is not in contact with the valve, the seal lip extends obliquely upward from the surface of the valve head toward the valve seat. For this reason, water adhering to the surface of the valve head opposing to the valve seat may be supported by the seal lip to stay on the surface of the valve head. This phenomenon may be generated, for example, when exhaust gas flows backwards through the check valve that is opened such that water contained in the exhaust gas adheres to the surface of the valve head. The water staying on the surface of the valve head may cause freezing or locking of the valve to restrict normal operation of the valve.